Catabolite Regulation of Enzymatic Activities in a White Pox Pathogen and Commensal Bacteria During Growth on Mucus Polymers from the Coral Acropora Palmata
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Vol. 87: 57–66, 2009 DISEASES OF AQUATIC ORGANISMS Published November 16 doi: 10.3354/dao02084 Dis Aquat Org Contribution to DAO Special 5 ’The role of environment and microorganisms in diseases of corals’ OPENPEN ACCESSCCESS Catabolite regulation of enzymatic activities in a white pox pathogen and commensal bacteria during growth on mucus polymers from the coral Acropora palmata Cory J. Krediet1, Kim B. Ritchie2, 3, Max Teplitski1, 3,* 1Interdisciplinary Ecology Graduate Program, School of Natural Resources and Environment, University of Florida, Institute of Food and Agricultural Sciences (IFAS), 103 Black Hall, PO Box 116455, Gainesville, Florida 32611, USA 2Mote Marine Laboratory, 1600 Ken Thompson Parkway, Sarasota, Florida 34236, USA 3Department of Soil and Water Science, University of Florida, IFAS, 106 Newell Hall, PO Box 110510, Gainesville, Florida 32611, USA ABSTRACT: Colonization of host mucus surfaces is one of the first steps in the establishment of coral- associated microbial communities. Coral mucus contains a sulfated glycoprotein (in which oligosac- charide decorations are connected to the polypeptide backbone by a mannose residue) and mole- cules that result from its degradation. Mucus is utilized as a growth substrate by commensal and pathogenic organisms. Two representative coral commensals, Photobacterium mandapamensis and Halomonas meridiana, differed from a white pox pathogen Serratia marcescens PDL100 in the pat- tern with which they utilized mucus polymers of Acropora palmata. Incubation with the mucus poly- mer increased mannopyranosidase activity in S. marcescens, suggestive of its ability to cleave off oligosaccharide side chains. With the exception of glucosidase and N-acetyl galactosaminidase, gly- cosidases in S. marcescens were subject to catabolite regulation by galactose, glucose, arabinose, mannose and N-acetyl-glucosamine. In commensal P. mandapamensis, at least 10 glycosidases were modestly induced during incubation on coral mucus. Galactose, arabinose, mannose, but not glucose or N-acetyl-glucosamine had a repressive effect on glycosidases in P. mandapamensis. Incubation with the mucus polymers upregulated 3 enzymatic activities in H. meridiana; glucose and galactose appear to be the preferred carbon source in this bacterium. Although all these bacteria were capable of producing the same glycosidases, the differences in the preferred carbon sources and patterns of enzymatic activities induced during growth on the mucus polymer in the presence of these carbon sources suggest that to establish themselves within the coral mucus surface layer commensals and pathogens rely on different enzymatic activities. KEY WORDS: Coral microbiology · Mucus surface polysaccharide · Coral pathogen Resale or republication not permitted without written consent of the publisher INTRODUCTION degrade components of the host surface-associated mucus (Vine et al. 2004, Fabich et al. 2008). In studies Attachment, colonization and establishment on host of bacteria associated with fish and corals, pathogens mucus surfaces are the first steps in the interactions rapidly degraded host surface mucus and reached high between bacteria and their eukaryotic hosts (Kurz et numbers (Vine et al. 2004, Sharon & Rosenberg 2008). al. 2003, Ritchie & Smith 2004, Rosenberg & Falkovitz When grown on host mucus in vitro, populations of 2004, Nehme et al. 2007). Pathogens and commensals commensal bacteria stabilized at densities that were at differ in the way they colonize host surfaces and least an order of magnitude lower than those reached *Corresponding author. Email: [email protected] © Inter-Research 2009 · www.int-res.com 58 Dis Aquat Org 87: 57–66, 2009 by pathogens (Vine et al. 2004). Similarly, Vibrio spp., lipids make up 4.2% of the mucus (Ducklow & Mitchell which are related to coral pathogens, dominated 1979, Meikle et al. 1988). The chemical composition of microbial communities formed on mucus of the coral the mucus glycoprotein differs among coral species Oculina patagonica after an extended incubation in (Ducklow & Mitchell 1979, Molchanova et al. 1985, vitro (Rosenberg & Falkovitz 2004, Sharon & Rosen- Meikle et al. 1987, 1988, Klaus et al. 2007). Mucus of berg 2008), even though vibrios make up less than 5% Acropora formosa, for example, contains 36 to 38% of culturable bacteria in the mucus layer of this coral neutral sugars, 18 to 22% amino sugars and 19 to 30% under normal conditions (Koren & Rosenberg 2006). amino acids (Meikle et al. 1988). The oligosaccharide Collectively, these observations support the hypothesis decorations (2 to 4 sugar residues in length) are that in the absence of other factors, opportunistic attached to the polypeptide backbone by an O-glyco- pathogens can overgrow and dominate coral-associ- sidic linkage to serine or threonine through the carbon ated microbial communities, thus contributing to the 1 of mannose (Meikle et al. 1987). The glycoproteins appearance of disease signs (Ritchie 2006). from A. formosa contain terminal arabinose residues This hypothesis also implies that opportunistic linked by a β 1→3 bond (Meikle et al. 1987). The entire pathogens of corals have the ability to outcompete spectrum of enzymatic activities involved in the degra- native coral-associated bacteria under the conditions dation of coral mucus by pathogenic, commensal and that favor this overgrowth. Consistent with this hypo- environmental bacteria is not yet characterized. thesis, of all the tested coral and environmental bacte- Preparations of coral mucus contain a significant ria, Serratia marcescens PDL100 reached the highest amount of low molecular weight compounds (Meikle et final population density when grown in vitro on mucus al. 1987, 1988, Krediet et al. 2009). While the chemical of Acropora palmata (Krediet et al. 2009). This strain of nature of these compounds is not yet known, the low S. marcescens was originally isolated as a cause of molecular weight fraction of mucus most likely contains white pox, a rapidly progressing coral tissue necrosis simple sugars and oligosaccharides that resulted from of the threatened Caribbean coral A. palmata (Patter- enzymatic degradation of the polymer. Even though son et al. 2002). The observations that the white pox these compounds appear to be plentiful in mucus, their strain was more efficient at utilizing mucus of the host effect on enzymatic activities in coral mucus-associated coral in vitro suggested that this ability to efficiently bacteria is not yet known. Kuntz et al. (2005) hinted at a degrade mucus may be linked to its pathogenicity potential role of sugars in coral ecology: exposure of (Krediet et al. 2009). coral fragments to sugars at 5 to 25 mg l–1 led to the ap- The mechanisms by which Serratia marcescens pearance of various disease signs. For example, a 30 d PDL100 colonizes, infects, and causes disease in corals treatment with lactose (at 25 mg l–1), a disaccharide that are not yet clear. The progression of infections caused by is not known to occur in the coral reef environment, led Serratia spp. in other invertebrates suggests that to nearly 100% mortality of the Montastraea annularis colonization of host surfaces is the first in a series of fragments; however, survivorship of Porites furcata was events leading to the appearance of disease signs. For only modestly reduced by the treatment (Kuntz et al. example, to cause disease in nematodes and flies, S. 2005). A 30 d incubation with mannose caused signifi- marcescens first colonizes the intestines, degrades cells cant mortality in P. furcata but not in M. annularis of the alimentary tract, and then spreads to other organs (Kuntz et al. 2005). It is not yet clear whether these ob- (Kurz et al. 2003, Nehme et al. 2007). Based on studies in served pathologies and mortalities were due to (1) the other invertebrates, it seems likely that S. marcescens destabilization of the symbiosis between the coral ani- PDL100 first needs to attach to and then establish itself mal and its photosynthetic dinoflagellates, (2) potential within the coral mucus surface layer. growth promotion of opportunistic pathogens by the The ability to utilize coral mucus as a growth sub- easily metabolizable carbon sources, or (3) a role of strate involves glycosidases, proteases and esterases these sugars in affecting virulence gene regulation in (Vacelet & Thomassin 1991, Krediet et al. 2009). These the existing microbial communities. enzymatic activities are generally consistent with the In order to better understand functions of carbon composition of coral mucus. The major component of sources in the behavior of coral-associated bacteria, the coral mucus surface layer is a sulfated glycopro- the present study tested the hypothesis that simple tein, and mucus also contains a significant amount of sugars, which would be released from the mucus gly- low molecular weight compounds that probably result coprotein by enzymatic digest, affect behaviors in- from microbial degradation of the polymers (Meikle et volved in the interactions of bacteria with mucus of the al. 1988). In mucus of acroporid corals, arabinose, N- coral host (e.g. enzymatic degradation and bacterial acetyl-glucosamine, mannose, glucose, galactose, N- attachment to mucus). acetyl-galactosamine and fucose are the major sugars; The results of the present study demonstrated signif- serine and threonine are the major amino acids; and icant differences in the sequence with which the white Krediet et al.: Catabolite regulation of mucus-degrading enzymes